MRI is an imaging method in which nuclear spin of an object placed in a static magnetic field is excited by an RF (Radio Frequency) signal having the Larmor frequency and an image is reconstructed based on MR (Magnetic Resonance) signals emitted from the object due to the excitation.
In recent MRI apparatuses, multiple receiving coils are commonly used. The multiple receiving coils are arranged around an object and MR signals received by these receiving coils are subjected to signal processing in a signal processing system disposed in the subsequent stage. The above-described receiving coil is also referred to as a surface coil.
As the number of receiving coils increases, the number of cables wiring each of the receiving coils to the signal processing system increases and thus handling of these cables becomes complicated. Therefore, instead of wired transmission, technology to wirelessly transmit signal transmission from each of the receiving coils to the signal processing system has been developed.
Moreover, from the view point of improving transmission quality of MR signals, technology to digitize analogue MR signals received by the receiving coils not in the signal processing system disposed in the subsequent stage but in each of the receiving coils has been considered. In this technology, digitized MR signals are wirelessly transmitted from each of the receiving coils to the signal processing system.
In order to perform A/D (analogue to digital) conversion in each of the receiving coils, a clock for A/D conversion (hereinafter, referred to as a reference clock) is necessary in each of the receiving coils. In this case, the following two types of configuration are possible. The one of them is to dispose a generation means of the reference clock inside each of the receiving coils (hereinafter, referred to as configuration by built-in clock type receiving coils). The other of them is to generate the reference clock in the signal processing system and transmit this reference clock to each of the receiving coils from the signal processing system (hereinafter, referred to as configuration by non-built-in clock type receiving coils).
In the configuration by built-in clock type receiving coils, distance between a sampling position of MR signals and a generation means of the reference clock can be shortened as compared with the configuration by non-built-in clock type receiving coils. Thus, in the configuration by built-in clock type receiving coils, transmission quality of the transmitted reference clock is hardly decreased and MR signals can be sampled with a high-quality reference clock.
Meanwhile, in the configuration by built-in clock type receiving coils, it is necessary to synchronize the reference clock between the respective receiving coils.
However, an MRI apparatus, which is equipped with plural built-in clock type receiving coils and can synchronize the reference clock for each of the built-in clock type receiving coils, has not necessarily been sufficiently studied.